What are you going to use it for? If just for informal target shooting, I'd go with the .260. If you reload, you can use .243 or .308 cases, but if .308's are used, you will have to turn the necks. Creedmoor ballistics are nearly identical to .260, but finding cases to reload can be iffy at times. If you are going to compete, then I'd go with the 6.5x284. It has proven itself as an exceptionally accurate cartridge, and can push the 142's around 200fps faster than the 260 or the Creedmore, but the tradeoff is less barrel life. That can be overcome to an extent by shooting slowly and not allowing the barrel to heat up. I bet you will enjoy whatever one of these you choose, for they're all excellent cartridges.